Microporous polyvinylidene fluoride (PVDF) hollow fibre membranes were spun using the dry-wet phase inversion method. By means of dip-coating technique, a uniform coating with thickness of around 5-12 μm of polyvinyl dimethylsiloxane (PVDMS) was formed on the surface of porous PVDF hollow fibers. The structural parameters of PVDF substrate membrane were estimated by gas permeation test. Using N2/O2 as the medium, the separation properties of PVDMS-PVDF composite hollow fiber membranes were also evaluated experimentally. The experimental data of both permeability and selectivity are in good agreement with the theoretical results predicted by the presented pore-distribution model. In order to obtain the compact composite membrane free of defects by the dip-coating technique, the thickness of PVDMS skin must be higher than 5 μm.